The well-conserved canonical and non-canonical Wnt pathways are important for all aspects of mammalian development, including the development of the central nervous system. An outstanding question remains: how are the various Wnt pathways that regulate development integrated in vivo? Dvls are outstanding candidates to address this question, since these conserved proteins are required in all eukaryotes for both canonical and non-canonical Wnt pathways. We have uncovered partially unique but predominantly redundant functions among the three Dvl genes. Single mutants display some unique defects in social behavior and conotruncal heart development, while double Dvl mutants display severe neural tube defects (craniorachischisis) and severe cochlear defects. In further support of redundancy, Dvl1/2/3 triple mutants are unable to undergo gastrulation and do not form mesoderm. We plan to dissect the in vivo pathways that Dvls regulate normal development and are disrupted in the Dvl mutants to produce these phenotypes. We produced in vivo conditional alleles in mice for each of the Dvl genes as well as in vivo alleles that can distinguish either canonical Wnt of non-canonical Wnt/PCP pathway function. We used these alleles to provide definitive evidence that the craniorachischisis phenotype displayed by Dvl1;Dvl2 double mutants resulted from disruption of convergent extension movements via the Wnt/PCP pathway. We will use these tools to provide a comprehensive analysis of the role of the canonical Wnt and non-canonical Wnt/PCP pathways during neuronal development from the first development of neural folds during gastrulation and neurulation throughout neurogenesis and neuronal migration. Based on our published and preliminary data, we predict that Dvls and the pathways they regulate are critical at all stages of brain development. We will use the following specific aims: 1) Determine the role of canonical Wnt and non-canonical Wnt/PCP pathways during gastrulation in vivo; 2) Characterize the Dvl dependent pathways responsible for neural tube closure during neurulation; 3) Determine the role of Dvls and the canonical Wnt and non-canonical Wnt/PCP pathways during forebrain/midbrain-hindbrain development using double Dvl mutants; and 4) Determine the role of Dvls and the canonical Wnt and non-canonical Wnt/PCP pathways during forebrain/midbrain-hindbrain development using triple Dvl mutants.